Hunter

The Hunter is a military helicopter.  It's very fast and maneuverable, and it has a machine gun and rockets.

One spawns at Verdant Meadows Airfield.

More info:
gta.wikia.com/wiki/Hunter
https://www.grandtheftwiki.com/Hunter

Cargobob

The Cargobob is a large military helicopter.

One spawns northeast of Las Venturas (but you pretty much need a helicopter or jetpack to get to it), and other one spawns in Area 69.

More info:
gta.wikia.com/wiki/Cargobob
https://www.grandtheftwiki.com/Cargobob

Stunt Plane

 

The Stunt plane is a small biplane.   It is very quick to take-off and very maneuverable (but twitchy).  Like the Cropduster you can make smoke trails with it.

One spawns at the Verdant Meadows Airfield.

More info:

gta.wikia.com/wiki/Stuntplane 

https://www.grandtheftwiki.com/Stunt_Plane 

Skimmer

The Skimmer is a Dodo with floats instead of wheels so it can land on water.  It's not really a good idea to land it on the ground as it just sort of slides.

One spawns across the bay from the boat school, and another one spawns north of the dam.

More info:
gta.wikia.com/wiki/Skimmer
https://www.grandtheftwiki.com/Skimmer

Shamal

The Shamal is a fairly small commercial jet.  You can find them at the three commercial airports.

More info:
gta.wikia.com/wiki/Shamal
 https://www.grandtheftwiki.com/Shamal

Rustler

The Rustler is a military plane.  It's equipped with machine guns.  It's sort of slow to take-off.

One spawns at Verdant Meadows Airfield.

More info:
gta.wikia.com/wiki/Rustler
https://www.grandtheftwiki.com/Rustler

Nevada

 

The Nevada is a large commercial plane.  It isn't a good idea to try to stuff it in the hanger.

One spawns at the San Fierro airport.

More info:
gta.wikia.com/wiki/Nevada
 https://www.grandtheftwiki.com/Nevada